Rubber vulcanization acceleration



tion accelerators.

2,983,716 RUBBER vvmrmzima ACCELERATION Ellis K. Fields, Chicago, Ill., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Filed Mar. 26, 1958, Ser. No. 723,986 j ew... or. 2604-795) This invention pertains to the vulcanization ofrubber, and more particularly relates to improved vulcaniza- An object of the present invention is toprovide anew 'and elfective class of rubber vulcanizationaccelerators,

which produce vulcanizates'having improved aging properties. Q I have found that effective rubber vulcanization accelerators are aromatic polysulfide-derivatives"of 2,5-dimercapto-l,3,4-thiadiazole having the general formula R-(S)x-S( l in'which R is an aryl radical, R' isthe hydrogen or an aryl radical which may be the same as R or a different ii-s mw aryl radical, x and y are numbers 0 to about 8, the sum of x and y being at least 1 and preferably 2 to about 16. The aryl radicals can be mono-or poly-nuclear and can have substituent groups such as hydrocarbon groups, halo, sulfo, etc. on the ring carbon atoms. Examples of such suitable aromatic radicals are phenyl, tolyl,,ben-

' y y yL na ht lii YLQ The" polysulfide derivatives of 2,5 -clim eroapto-l,3,4- thiadiazole can be suitably prepared by severalmethods. For example; they can be prepared by reacting the thiadiazole with a suitable arylsulfenyl halide in a 1:1 molar proportion at -10 C. to.215 C. for 1 to 6 hours in the presence of a solvent. suchas chloroform or carbon tetrachloride. Preferably, however,-I"pr'efer to prepare. the polysulfides by reacting .the 2,5-dimercapto-1,3,4-thiadiazole with an aromatic mercaptan and sulfur in the molar proportions of 31:1:1 to1:2:4 respectively at 100-150 C. for 1 to 6 hours. If desired, a solvent such as Cellosolve or xylene can be used. Bis-trisulfide derivatives are obtained by reacting the 2,5-dimercapto- 1,3,4-thia diazole with an aryl mercaptan and a sulfur chloride inmolar ratios of from 1:212 to 1:2:4 respectivelyat a temperature of 50-100 C. Higher polysulfides can be prepared by reacting the thiadiazole dior trisulfides with' sulfur at temperatures of ZOO-400 F.

The preparation of the polysulfide derivatives of 2,5- mercapto-1,3,4-thiadiazole is illustrated by the following examples; EXAMPLE I The vapor from 4.59 ml. (7.09 grams, 0.1 mole) chlorine was passedinto a solution of,10.26 ml. (11.02 grams, 0.1 mole) thiophenol in 100 ml. carbon tetrachloride stirred at 5 C. Afterall the chlorine was in, the mixture was stirred for 15 minutes at 0 C., then treated portionwise with 15 grams (0.1 mole) 2,5-dimercapto- 1,3;4-thiadiazoleover BO minutes, maintaining thegtemperature at -5 C. to --0 C. The mixture was then allowed to warm to room temperature, and finally stirred at 45 C. with N blowing for 2 hours. Evaporation of the solvent on a steam bath gave a yellow solid which crystallized from benzene and melted at 140.5-141" C.

, 2,9s3;71s lfatented May 9, I 1961 The yield wasl figrams lated for C H N S N,10.85; S, 49.60; mol. wt., 258. Found: N, 10.62; S, 49.50;11101. wt., 268.

EXAMPLE II A mixture of 41 ml. (44 grams, 0.4 mole) thiophenol, 30 grams (0.2 mole) 2,5-dimercapto-1,3,4-thiadiazole, 12.8 grams (0.4 gram atom) sulfur, and 60 ml. xylene was stirred at 125 C. for 4 hours, cooled, the light yellow solid collected on a filter and crystallized from benzene. There resulted 52 grams solid melting at 124-128 C. and containing 12.13% N and 42.3% sulfur.

EXAMPLE HI A mixture of 109 grams fuel oil thiocresols (obtained by springing alkaline wash from fuel oils with HCl and distilling, b.p. -110/3.2, 11.12% sulfur), 30 grams (0.2 mole) 2,5-dimercapto-1,3,4-thiadiazole and 12.8 grams (0.4 gram atom) sulfur was stirred at 130-135 C. for 2 hours. Hydrogen sulfide evolved and the 2,5-dimercapto-1,3,4-thiadiazole went into solution. The product was cooled and filtered, giving 129 grams viscous yellow product containing 3.47% N and 26.0%

sulfur.

EXAMPLE IV tion can be used singly or in admixtures with each other,

to vulcanize natural rubber, synthetic rubbers and other vulcanizable organic materials such as balata, gutta percha and the like, which are susceptible to vulcanization when heated with from 1% to about 5% sulfur. The accelerators of this invention used in amounts of from about 0.1% to about 3%, based on the rubber in the composition, can be employed together with other materials such as antioxidants, retarders, softeners",

fillers, etc.

To demonstrate the effectiveness of the herein described vulcanization accelerators, a GR-S rubber (a Lbutadiene-styrene copolymer) was blended in a standard formula as follows:

. i V A Parts byweight GR -S' PhilblackO (carbon) 50 Zinc oxide 5 Stearic acid 2 Sulfur L... 1.75 Antioxidant (Betanox Special) 1 1 A. ketone-amine condensation product marketed by Nougatauclr Chemical.

.To the above formulationwas added 1.75 parts of the 2.swdimercaptoe1,3,4-thiadiazole polysulfide; of Example II; this formulation is identified asFormulaNo. 1 in the tabulation below. For comparison, to the same basic formula, in place of; the accelerator of the present invention wasr added 1.75 parts .2,2 '-dithiobisbenzothiazole (Formula 2), Z-mercaptdbenzothiazole (Formula 3), and N-cyclohexyl-Z-benzothiazole-sulfenamide (Formula 4). The later three compounds are commercial vulcanization accelerators in common use at present.

The four formulations were cured at 316 F. for 5,

(64% Analysis.Calcu- 10, 15, 25, 30 and 40 minutes and the physical properties i physical properties thereof again determined.

The data obtained are tabulated in TableI.

n TableI- Cure at Mod. Tens, Percent Lbs. Formula No. 6 F., 200 p.s.i. Elong. Hard. Tear.

Minutes OVEN AGED HOURS AT 12 F.

In the table, above, the various column headings have the following meanings:

Mod. 200%--The value of the load in pounds per square inch of original cross-section area of sample to give an elongation of 200%.

Tens. p.s.i.The pounds per square inch of original cross-section when the test piece of rubber breaks at an elongation of 20 inches per minute speed.

Elong.The percentage of elongation of the test piece at breaking point. I r

Hard.A measure of thehardness of the rubber in resisting the indentation of its surface by a cone.

Lbs. Tear--Pounds of force which must be applied to a notched piece of'rubber to tear it apart.

The first three tests were conducted on a Scott Testing Machine Model 6 according to ASTM D-412-51T; hardness was measured by a Shore Durameter Type A, ac-

cording to ASTM D-314-52T; and the tear test was Products.

Percentages given herein and in the appended claims are weight percentages, unless otherwise stated.

I claim: p

' 1. The method which comprises vulcanizing a rubber selected from the class consisting of natural rubber and butadiene-styrene copolymer synthetic rubber in the presence of from 1% to about 5%, based on the rubber, of sulfur, and from about 0.1% to about 3%., based on the rubber, of a polysulfide derivative of 2,5-dimercapto- 1,3,4-thiadiazole having the general formula phenyl radicals.

4. The method of claim 1 in which R is a phenyl radi- .cal, R is hydrogen, at is 1 and y is 0.

5. The method of claim 1 in which R and R are ring .alkylated phenyl radicals.

6. An unvulcanized composition containing a predominant amount of a rubber selected from the class consisting of natural rubber and butadiene-styrene copolymer synthetic rubber, from about 1% to about 5%, based on the rubber, of sulfur and from about 0.1% to about 3%, based on the rubber, of a polysulfide derivative of 2,5-dimercapto-1,3,4-thiadiazole having the general formula 40 in which R is an aryl radical, R is selected from the y, are integers 0 to about 8, the sum of x and y being group consisting of hydrogen and an aryl radical, x and and y is O.

9. An unvulcanized composition as described in claim 6 in which R and R. are phenyl radicals.

10. The method of claim 1 in which the rubber is :natural rubber.

11. An unvulcanized composition as described'in'clairn 6 in whichthe rubber is natural rubber.

12. An unvulcanized composition as described in claim 6 in which Rand R arering alkylated phenyl radicals.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD WHICH COMPRISES VULCANIZING A RUBBER SELECTED FROM THE CLASS CONSISTING OF NATURAL RUBBER AND BUTADIENE-STYRENE COPOLYMER SYNTHETIC RUBBER IN THE PRESENCE OF FROM 1% TO ABOUT 5%, BASED ON THE RUBBER, OF SULFUR, AND FROM ABOUT 0.1% TO ABOUT 3%, BASED ON THE RUBBER, OF A POLYSULFIDE DERIVATIVE OF 2,5-DIMERCAPTO1,3,4-THIADIAZOLE HAVING THE GENERAL FORMULA 